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(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K ? (b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools ? Explain. (c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature? (d) What is the effect of change of temperature on the solubility of a salt ?

Q.3:- Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in the following table, as grams of substance dissolved in 100 grams of water to form a saturated solution).

Substance Dissolved

Temperature in K

283

293

313

333

353

Potassium nitrate

Sodium chloride

Potassium chloride

Ammonium chloride

(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K ?
(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools ? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a salt ?

Answer:-

(a) Solubility of potassium nitrate at 313K = 62/100

100 g of water contains potassium nitrate = 62 g

50 g of water contains potassium nitrate = 62/100 X 50 = 31g

Thus, 31 g potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 g of water at 313 K.

(b) When a saturated solution of potassium chloride at 353 K is cooled, the solubility potassium chloride in water decreased. As a result the amount of potassium chloride which exceeds its solubility at lower temperature separates out as crystals.

(c) The maximum amount of the salt which is dissolved in 100 g of water to form a saturate solution at the given temperature is known as solubility.

Solubility of potassium nitrate at 293 K = 32/100

Solubility of sodium chloride at 293 K = 36/100

Solubility of potassium chloride at 293 K = 35/100

Solubility of ammonium chloride at 293 K = 37/100

From the above data it is clear that ammonium chloride has the highest solubility at 293 K

(d) In general the solubility of a salt increases with temperature. The increase is however different for different salts. For example the solubility of potassium nitrate increase appreciably that of ammonium chloride increases slightly that of potassium chloride increases marginally while that of sodium chloride almost remains constant.